All-wheel drive capable vehicles have many advantages over vehicles having a driveline connected to only a single axle. Specifically, all-wheel drive capable vehicles have increased traction and enhanced drivability over similar vehicles that are driven using only a single axle.
However, traditional all-wheel drive vehicles are disadvantaged by requiring continuous rotation of a second drive axle, and other portions of the driveline, at road speed, even when the all-wheel drive functionality is not beneficial. Consequently, traditional all-wheel drive vehicles tend to have reduced fuel, and overall, efficiency when compared to vehicles having only a single drive axle.
All-wheel drive vehicles are increasingly equipped with a secondary driveline disconnect feature. In such vehicles, when a control system detects that all-wheel drive functionality is not required, the control system disconnects the second drive axle (and other associated driveline components) to place the driveline into a single axle drive mode. Once the second drive axle is disconnected, there is no transfer of torque to the second drive axle. As a result, speed-dependent losses associated with the second drive axle (and other associated driveline components) are eliminated by allowing the second drive axle (and other associated driveline components) to remain in an idle condition. A secondary driveline disconnect feature may also allow a control of the torque delivered by the secondary axle. The former aids in decreasing the vehicle's fuel consumption, and the latter provides a very flexible torque control.
Typically, as part of a AWD system connect event, a secondary driveline disconnect propeller shaft rotational speed measurement is performed by measuring the time between the passing of two teeth of a rotating part such as a gear or tone wheel. In the known method, the rotational distance between two teeth of the rotating part is accurately known. The known method includes measuring two subsequent rising edges or two subsequent falling edges of teeth on the rotating part. Dividing the known position increment by the time provides an estimate of the propeller shaft rotational speed. Alternatively, a pulse counter can be used to account for the number of pulses in a given sampling period.
However, this method results in delayed and inaccurate measurements, especially at low propeller shaft rotational speeds, i.e., a low pulse count. The challenge remains to have an all-wheel drive vehicle which transitions from the disconnected (two-wheel drive) state to the connected (four-wheel drive) state in such a way that the vehicle operator does not feel the transition from two-wheel drive to four-wheel drive.
The disclosure herein describes a method and system for actuating a clutch utilizing an adaptable model and a high resolution measurement of the rotational speed of a propeller shaft.